It is well known that the quality of water typically supplied to households from private sources or municipal water treatment plants and the like can be improved by the filtration therefrom of various contaminants. These contaminants can take on a variety of forms, including relatively large particles such as sand, inorganic materials including such things as lead, mercury, iron, and nitrates, which are associated with "hard" water, and organic compounds of wide variety, as well as tiny pathogens such as bacteria, spores and the like. It is known to employ differing filters to filter out such differing contaminants, and as much as many devices claim to supply "pure" water, this is the only unit of its type which can be demonstrated to meet U.S. standards for "potable" drinking water.
The prior art shows a wide variety of elaborate devices designed to purify water. None of these are as suitable as would be desired. For example, various prior art devices are unduly expensive, are of great complexity, require supply of electrical power, have operator training requirements and use undesirable chemical bactericidal techniques, or are simply unreliable, as well as varying combinations of these. These processes include such things as reverse osmosis filtering, and distillation processes, all of which are, as noted, generally too complicated and expensive for the average homeowner even in the United States, and are much less suitable for developing and Third World nations, where simplicity and low cost are crucial to the success of any drinking water purification unit. Others, such as compressed carbon filters have inadequate protection against plugging and insufficient reliability for the removal of pathogens.
It is also important in a water purifier for home use that means be provided to sterilize any bacteria which do survive the filtration process and moreover that no breeding ground for bacteria be established downstream from the bacterial filter, which has, in fact, occurred with certain prior art designs.
It is clear, therefore, that a need exists for an improved and reliable purification device.
Another factor which requires consideration in the design of a water purification device, particularly for household use, is that it be easy to install and simple to service. Prior art multiple filter designs have necessitated the mounting and connection by plumbing of plural containers containing the plural types of filters, which is sufficiently complex to dissuade many householders from attempting to attach water purification systems in their home drinking water supply systems. Moreover, such plural containers are wasteful of space and cost more than would a single container containing all types of filters necessary for adequate water purification.
The design of a successful water filter containing plural media for filtration purposes also involves selection of the relative amounts of media contained and their arrangement in such a way that the water is presented to each for an appropriate amount of time such that the respective contaminants can effectively be removed by each filter. For example, in the case of an activated carbon filter, the critical issue to ensure proper carbon adsorption of impurities is the contact time of the influent water to the carbon. This is a function of flow rate, the volume of carbon available and the design of the filter itself. Many prior art carbon filters as documented by reports done for the Office of Drinking Water U.S. Environmental Protection Agency under Contract No. 68-01-4766, have too large a flow rate in relation to the volume of carbon contained therein and do a poor job. Others are badly designed and do not ensure that the water flows evenly through the filter so that inconsistent results are obtained. Carbon filters also provide a potential breeding ground for bacteria and although some manufacturers use silver, a known bacteriostatic agent, in their carbon filters, none have shown positive results in reducing bacterial contamination. As in the case of carbon adsorption, silver sterilization of bacteria requires both a relatively long contact time and a proper water pH level, for effectiveness.
It is known to use a ceramic microscreen to screen out such things as bacteria, spores and other pathogens and to impregnate this with bacteriostatic silver. However, it is important that this ceramic filter be placed in the water flow pattern at a point where it will have the maximum effectiveness, and this has not always been done in the prior art. One prior art design even places a carbon core within a cylindrical ceramic microscreen to reduce bad taste and odor, thus providing a bacteria breeding ground placed in the water flow pattern after the ceramic bacteria filtering stage.